The carboxylic acid derivatives VIII! are useful as agricultural fungicides or their intermediates (JP-A 4-295454), and as the process for their production, it has been known that they can be produced by the following route in which metal salts of phenol derivatives of the general formula I!: ##STR3## wherein R.sup.1 and R.sup.2 are each as defined above and A is an alkali metal or an alkaline earth metal, are used as the staring material (JP-A 4-295454): ##STR4##
However, when the carboxylic acid derivatives VIII! are produced by such a process, the reaction in the step (i) is effected at a high temperature such as 200.degree. C., which requires factory facilities for use as a heating source, such as high-pressure steam equipment or high-temperature heat medium control equipment, or the reaction in the step (iv) is effected under cooling below 0.degree. C., which requires various facilities such as freezing machines. This process is, therefore, not a satisfactory process from an industrial point of view.
Further, in this process, different solvents are used in the respective steps: for example, methanol in the step (i); toluene in the steps (ii) and (iii); methyl t-butyl ether and methanol (reaction solvent) as well as dichloromethane (extraction solvent) in the step (iv); and methanol and dichloromethane (reaction solvent) in the step (v). In addition to such a complicated feature that various kinds of solvents are used in the production on an industrial scale, there is another disadvantage that it requires solvent recovery facilities and numerous solvent storage tanks, in which respect the above process is not satisfactory as an industrial production process.